/* 
  1.该文件是用于创建一个为Count组件服务的reducer，reducer的本质就是一个函数
  2.reducer函数会接到两个参数，分别为：之前的状态(preState)，动作对象(action)
*/

import { INCREMENT, DECREMENT } from './constant'

// 初始化state
const initState = 0

export default function countReducer(preState = initState, action) {
  // console.log(preState, action)

  const { type, data } = action
  switch (type) {
    case INCREMENT:
      return preState + data
    case DECREMENT:
      return preState - data
    default:
      return preState
  }
}
